1. Field of the Invention
One embodiment of the present invention relates to a light-emitting device, a display device, a display module, a lighting module, an electronic device, and a lighting device. Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, a method of driving any of them, and a method of manufacturing any of them.
2. Description of the Related Art
As next generation lighting devices or display devices, display devices using light-emitting elements (organic EL elements) in which organic compounds are used as light-emitting substances have been developed or commercialized because of their potential for thinness, lightness, flexibility, high speed response to input signals, low power consumption, and the like.
In an organic EL element, voltage application between electrodes, between which a light-emitting layer is interposed, causes recombination of electrons and holes injected from the electrodes, which brings a light-emitting substance (an organic compound) into an excited state, and the return from the excited state to the ground state is accompanied by light emission. Since the spectrum of light emitted from a light-emitting substance depends on the light-emitting substance, use of different types of organic compounds as light-emitting substances makes it possible to obtain light-emitting elements which exhibit various colors.
The lifetime and reliability are important characteristics of such light-emitting elements.
Patent Document 1 focuses on a halide contained in an organic compound included in an EL layer and discloses a light-emitting element with a long lifetime obtained by limiting the concentration of halides to a certain level.
Patent Document 2 discloses that the lifetime is adversely affected by the amount of halogen compounds in a light-emitting layer and a layer adjacent to the light-emitting layer (specifically, a light-emitting region) in an EL layer and that the lifetime is not largely affected by halides contained in a hole-injection layer apart from the light-emitting region even when the amount of the halides is large to some degree.